Tumour necrosis factor alpha (TNFα, also known as cachectin), is a naturally occurring mammalian cytokine produced by numerous cell types, including monocytes and macrophages in response to endotoxin or other stimuli. TNFα is a major mediator of inflammatory, immunological, and pathophysiological reactions (Grell, M., et al. (1995) Cell, 83: 793-802).
Soluble TNFα is formed by the cleavage of a precursor transmembrane protein (Kriegler, et al. (1988) Cell 53: 45-53), and the secreted 17 kDa polypeptides assemble to soluble homotrimer complexes (Smith, et al. (1987), J. Biol. Chem. 262: 6951-6954; for reviews of TNFA, see Butler, et al. (1986), Nature 320:584; Old (1986), Science 230: 630). These complexes then bind to receptors found on a variety of cells. Binding produces an array of pro-inflammatory effects, including (i) release of other pro-inflammatory cytokines such as interleukin IL-6, IL-8, and IL-1, (ii) release of matrix metalloproteinases and (iii) up regulation of the expression of endothelial adhesion molecules, further amplifying the inflammatory and immune cascade by attracting leukocytes into extravascular tissues.
A large number of disorders are associated with elevated levels of TNFα, many of them of significant medical importance. TNFα has been shown to be up-regulated in a number of human diseases, including chronic diseases such as rheumatoid arthritis (RA), inflammatory bowel disorders including Crohn's disease and ulcerative colitis, sepsis, congestive heart failure, asthma bronchiale and multiple sclerosis. Mice transgenic for human TNFα produce high levels of TNFα constitutively and develop a spontaneous, destructive polyarthritis resembling RA (Keffer et al. 1991, EMBO J., 10,4025-4031). TNFα is therefore referred to as a pro-inflammatory cytokine.
TNFα is now well established as key in the pathogenesis of RA, which is a chronic, progressive and debilitating disease characterised by polyarticular joint inflammation and destruction, with systemic symptoms of fever and malaise and fatigue. RA also leads to chronic synovial inflammation, with frequent progression to articular cartilage and bone destruction. Increased levels of TNFα are found in both the synovial fluid and peripheral blood of patients suffering from RA. When TNFα blocking agents are administered to patients suffering from RA, they reduce inflammation, improve symptoms and retard joint damage (McKown et al. (1999), Arthritis Rheum. 42:1204-1208).
Physiologically, TNFα is also associated with protection from particular infections (Cerami. et al. (1988), Immunol. Today 9:28). TNFα is released by macrophages that have been activated by lipopolysaccharides of Gram-negative bacteria. As such, TNFα appears to be an endogenous mediator of central importance involved in the development and pathogenesis of endotoxic shock associated with bacterial sepsis (Michie, et al. (1989), Br. J. Surg. 76:670-671.; Debets. et al. (1989), Second Vienna Shock Forum, p. 463-466; Simpson, et al. (1989) Crit. Care Clin. 5: 27-47; Waage et al. (1987). Lancet 1: 355-357; Hammerle. et al. (1989) Second Vienna Shock Forum p. 715-718; Debets. et al. (1989), Crit. Care Med. 17:489-497; Calandra. et al. (1990), J. Infect. Dis. 161:982-987; Revhaug et al. (1988), Arch. Surg. 123:162-170).
As with other organ systems, TNFα has also been shown to play a key role in the central nervous system, in particular in inflammatory and autoimmune disorders of the nervous system, including multiple sclerosis, Guillain-Barre syndrome and myasthenia gravis, and in degenerative disorders of the nervous system, including Alzheimer's disease, Parkinson's disease and Huntington's disease. TNFα is also involved in disorders of related systems of the retina and of muscle, including optic neuritis, macular degeneration, diabetic retinopathy, dermatomyositis, amyotrophic lateral sclerosis, and muscular dystrophy, as well as in injuries to the nervous system, including traumatic brain injury, acute spinal cord injury, and stroke.
Hepatitis is another TNFα-related inflammatory disorder which among other triggers can be caused by viral infections, including Epstein-Barr, cytomegalovirus, and hepatitis A-E viruses. Hepatitis causes acute liver inflammation in the portal and lobular region, followed by fibrosis and tumor progression. TNFα can also mediate cachexia in cancer, which causes most cancer morbidity and mortality (Tisdale M. J. (2004), Langenbecks Arch Surg. 389:299-305).
The key role played by TNFα in inflammation, cellular immune responses and the pathology of many diseases has led to the search for antagonists of TNFα. One class of TNFα antagonists designed for the treatment of TNFα-mediated diseases are antibodies or antibody fragments that specifically bind TNFα and thereby block its function. The use of anti-TNFα antibodies has shown that a blockade of TNFα can reverse effects attributed to TNFα including decreases in IL-1, GM-CSF, IL-6, IL-8, adhesion molecules and tissue destruction (Feldmann et al. (1997), Adv. Immunol. 1997:283-350). Among the specific inhibitors of TNFα that have recently become commercially available include a monoclonal, chimeric mouse-human antibody directed against TNFα (infliximab, Remicade™; Centocor Corporation/Johnson & Johnson) has demonstrated clinical efficacy in the treatment of RA and Crohn's disease. All marketed inhibitors of TNFα are administered intravenously or subcutaneously in weekly or longer intervals as bolus injections, resulting in high starting concentrations that are steadily decreasing until the next injection. Their volume of distribution is limited.
Despite these advances, there remains a need for new and effective forms of antibodies or other immunobinders for the treatment for TNFα-associated disorders such as RA. In particular, there is an urgent need for immunobinders with optimal functional properties for the effective and continuous treatment of arthritis and other TNFα-mediated disorders which allow for more flexible administration and formulation and have an improved tissue penetration and thereby an increased volume of distribution.